Conventionally, there has been known a fin and tube heat exchanger composed of a combination of a plurality of plate-shaped fins which are stacked at predetermined fin pitches and heat transfer tubes having a flattened shape with a substantially elliptical or substantially oval cross-section. Such a heat exchanger is configured, for example, to include: a plurality of plate-shaped fins which are stacked at predetermined fin pitches, each of the plate-shaped fins being provided with a plurality of notches at end portions thereof in a longitudinal direction; and a plurality of heat transfer tubes having a flattened shape, each of which is extended in a stacking direction of the plate-shaped fins, each of the heat transfer tubes being disposed in a corresponding one of the notches. Further, each of the heat transfer tubes has end portions connected to a distribution pipe or a header that is combined with these heat transfer tubes to form a refrigerant flow passage. Moreover, such a heat exchanger is designed to exchange heat between a heat exchange fluid such as air that flows through the plate-shaped fins and a heat exchanged fluid such as water or refrigerant that flows inside of the heat transfer tubes having a flattened shape.
A heat exchanger such as that described above is configured such that to improve close contact between the plate-shaped fins and the heat transfer tubes, each of the plurality of plate-shaped fins includes, at circumferential portions thereof defining the notches, fin collars which are raised perpendicularly from the circumferential portions and brought into contact with the heat transfer tubes either by furnace blazing or with an adhesive. Further, a heat exchanger such as that described above is known to be configured such that to improve heat exchanging performance of the plate-shaped fins, each of the plurality of plate-shaped fins includes, in regions thereof between the notches, lugs called slits bored in a mainstream direction of air or asperities called scratches in the mainstream direction of air. Further, a heat exchanger such as that described above is known which, to improve the heat exchanging performance, includes heat transfer tubes having a plurality of flow passages formed inside or heat transfer tubes having grooves formed in inner surfaces thereof.
Further, a conventional heat exchanger such as that described above which includes heat transfer tubes having a flattened shape is configured such that the pitches at which the plurality of plate-shaped fins are stacked are held constant and positioning is facilitated by cutting and raising parts of the plate-shaped fins to form spacers and bringing the spacers into contact with base surfaces of the adjoining fins in stacking the fins (see Patent Literature 1).
Further, a conventional heat exchanger such as that described above which includes heat transfer tubes having a flattened shape is configured such that the pitches at which the plurality of plate-shaped fins are stacked are held constant and positioning is facilitated by bending tip portions of those parts of the fin collars, which are raised perpendicularly from the circumferential portions of the plate-shaped fins defining the notches, outward to provide rectangular protruding sections called reflares and making these reflare sections have a height of bending that determines the fin pitches between the plate-shaped fins bringing the reflares into contact with base surfaces of the adjoining fins in stacking the fins (see Patent Literature 2).